(This communist fundie is talking about the Holodomor and the population transfers, i.e. Stalin's forced relocation and genocide-by-starvation against the Ukrainian people.)

It's bourgeois propaganda created by the imperialist states to discredit the USSR. There is not a shred of evidence Stalin committed genocide. Usually this charge is made against the Holodomor, of which not even bourgeois historians are in agreement that it was genocide. They were done because of significant Nazi collaborators and counter-revolutionaries among those who were transferred. While there were obvious unfortunate costs with this, it was necessary to preserve the integrity of the proletarian state. It was the best possible decision in a very difficult period.